A long RP tachycardia with the earliest atrial activation at the His
bundle region : What is the mechanism?
A 72-year-old female with frequent palpitation was referred for
radiofrequency ablation. The baseline 12-lead electrocardiogram and
echocardiography results were normal. At baseline, the atrio-His (AH)
and His-ventricular (HV) intervals were 90 and 41 ms, respectively. Dual
atrioventricular (AV) nodal physiology or ventriculoatrial (VA)
conduction was not observed during programmed atrial and ventricular
stimulation. After isoproterenol infusion, VA conduction became
decremental and concentric, with the earliest atrial activation seen at
the His bundle (HB) region during ventricular pacing. A supraventricular
tachycardia with a long RP interval (SVT) was induced by atrial
extra-stimulation, without any jump-up in the AH interval. During the
SVT, the AH and HV intervals were 180 and 180 ms, respectively, and the
earliest atrial activation was recorded in the HB region (Figure 1A).
During the SVT, transient 2:1AV conduction was observed (Figure 1B).
Ventricular overdrive pacing at a pacing cycle length (CL) of 360 ms was
performed during the SVT with a CL of 390ms (Figures 2A and B). Based on
these observations, what is the mechanism of this tachycardia?